1. Field of the Invention
The present invention relates to a pressure sensor having a capacitive pressure transducer.
2. Description of the Related Art
FIG. 1 shows a longitudinal section of a conventional pressure sensor of the above-mentioned type.
A housing 10 of the conventional pressure sensor has a metallic first cap-like half housing 10a. A fluid inlet channel 10b is formed at a top portion of the first half housing 10a so as to be adapted to communicate with a fluid passage (not shown).
An enlarged opening of the first half housing 10a is airtightly closed by a substantially disc-shaped capacitive pressure transducer 14 with an O-ring 12 interposed therebetween. The capacitive pressure transducer 14 has two rod-shaped electric terminals 14a extending in a direction away from the fluid inlet channel 10b of the first half housing 10a.
An annular spacer ring 16 made of non-conductive plastic material is placed on a peripheral edge portion of the side surface of the capacitive pressure transducer 14, which does not face to the fluid inlet channel 10b of the first half housing 10a. A circuit board 18 is supported on a side surface of the spacer ring 16 which does not face to the capacitive pressure transducer 14.
Two electric terminals 14a of the capacitive pressure transducer 14 are inserted into two electric connection holes formed at predetermined positions of the circuit board 18, and electrically connected to an electric circuit formed on the circuit board 18.
The spacer ring 16 produces a predetermined space between the circuit board 18 and the capacitive pressure transducer 14. On the surface of the circuit board 18 facing to the capacitive pressure transducer 14 and on another surface thereof not facing to the transducer 14, there are arranged various electric or electronic parts 18a for performing a predetermined electronic signal processing based on a pressure corresponding electric signal sent from the capacitive pressure transducer 14.
At a plurality of predetermined positions of the surface of the circuit board 18 not facing to the capacitive pressure transducer 14, there are provided a plurality of sockets 18b for transmitting the electric signal from the circuit board 18.
A peripheral edge portion of an enlarged opening of a second cap-like half housing 10c made of non-conductive plastic material is placed on the peripheral edge portion of the surface of the circuit board 18 not facing to the capacitive pressure transducer 14. Various electric or electronic parts 18a and the plurality of sockets 18b on the surface of the circuit board not facing to the capacitive pressure transducer 14 are contained in an inner space of the second half housing 10c. A plurality of outer connection terminals 20 are supported at predetermined positions of the top portion of the second half housing 10c to be opposite to the plurality of sockets 18b, and long and thin base end portions 20a of the plurality of outer connection terminals 20 are inserted into the plurality of sockets 18b.
The spacer ring 16 and the second half housing 10c are surrounded by a skirt portion extending from the periphery of the enlarged opening of the first half housing 10a in a direction away from the fluid inlet channel 10b. The second half housing 10c is connected to the first half housing 10a by engaging the extending end of the skirt portion of the first half housing 10a with a shoulder formed on the peripheral surface of the second half housing 10c. Thereby, the second half housing 10c and the first half housing 10a sandwich the spacer ring 16. Moreover, the spacer ring 16 and the peripheral edge portion of the enlarged opening of the first half housing 10a sandwich the O-ring 12 and the peripheral edge portions of both side surfaces of the capacitive pressure transducer 14. Furthermore, the spacer ring 16 and the peripheral edge portion of the enlarged opening of the second half housing 10c sandwich the peripheral edge portions of both side surfaces of the circuit board 18.
The plurality of outer connection terminals 20 of the top portion of the second half housing 10c extend in a direction away from the top portion along a longitudinal center line of the second half housing 10c, and are surrounded with a socket guiding cylindrical portion 22 formed on the top portion.
In the area of the ton portion, surrounded by the socket guiding cylindrical portion 22, openings 24 are formed to be opposed to the predetermined electric or electronic parts 18a of the circuit board 18 contained in the inner space of the second half housing 10c. The openings 24 are covered with a dust and water proof cap 26, and the predetermined electric or electronic parts 18a can be adjusted from the outer space through the openings 24 after detaching the dust and water proof cap 26.
The above-structured conventional pressure sensor is formed as follows. First, the spacer ring 16 is sandwiched by the capacitive pressure transducer 14 and the circuit board 18, then the transducer 14 and the circuit board 18 are electrically connected to each other, and finally a spacer ring unit is structured. The first half housing 10a and the second half housing 10c are mutually connected to each other in a state that the spacer ring unit is sandwiched therebetween. Thereby, the assembly of the pressure sensor is finished.
However, in such a conventional pressure sensor, the two electric terminals 14a of the capacitive pressure transducer 14 are easily bent. Also, it is difficult to obtain high positional accuracy of the terminals 14a. Therefore, the electrical connection between the capacitive pressure transducer 14 and the circuit board 18 through the terminals 14a in the state that the spacer ring 16 is sandwiched therebetween is manually performed.